At present, pharmaceutical products are coated with materials of various kinds, for example a liquid substance, using a hollow drum or rotary pan consisting basically of a hollow cylindrical body having end portions shaped substantially like truncated cones. The products to be coated are placed inside the drum and a coating solution is applied to them, for example by spraying.
The drum is rotated continuously so as to mix the products well and a stream or flow of air is circulated inside the drum in order to dry the solution to form the product coating.
At present, drums or pans for coating units can be divided broadly into two types.
In a first type of pan or drum, known in the trade as a Pellegrini pan, the air used for drying purposes is circulated by means of a pair of perforated tubes which are mounted at an angle inside the pan and which, in use, are partly immersed in the mass of products being coated. The inside surfaces of the pan have mixing blades mounted on them to improve the mixing effect while the pan is rotated.
Rotary drums or pans of this kind have been used in product coating devices for some time with excellent results, especially if the speed at which the pan is rotated is not too high.
In the second known type of coating pan, the central body of the hollow pan has a plurality of holes distributed on its cylindrical surface, through which the air used to dry the coating material flows. The deflecting/mixing blades, on the other hand, are located on both the truncated cone portions. Each blade is fixed at one end to the wall of the pan and extends with its other end towards the central cylindrical part.
This solution, however, suffers from a considerable drawback, especially when the pan is rotated at high speeds and that is, that the projecting blades are not able to mix the product very effectively, which means that many of the products are not properly coated and must be rejected.
In addition, the projecting configuration of the deflecting/mixing blades makes it difficult to clean the pan, especially because product fragments tend to accumulate in corners and recesses where the blades are attached to the pan and which are difficult to see and access.